1. FIELD OF THE INVENTION
The present invention relates to a coater apparatus for applying a primary flow of coating material to a moving web of paper. More particularly, the present invention relates to a coater apparatus which includes a backing blanket disposed on the opposite side of the paper web relative to a short dwell coater.
2. INFORMATION DISCLOSURE STATEMENT
Short dwell coaters are capable of coating a web of paper at speeds of 3,000 feet per minute and upwards thereof.
A short dwell coater essentially includes a housing defining a coating chamber and having an inlet connected to a supply of coating material and an outlet disposed adjacent to a moving web of paper. Pressurized coating material flows through the coating chamber and through the outlet where such coating material comes into intimate contact with an adjacent surface of the moving web of paper. A flexible metering blade is disposed immediately downstream relative to the outlet so that coating material applied to the surface of the paper web is metered and smoothed onto the web. In view of the relatively short residence time of any point on the moving web contacting the outlet, such coaters have been termed "short dwell coaters". Such "short dwell" or resident time inhibits excessive absorption of the coating material into the moving web. Consequently, such short dwell coaters not only reduce the amount of coating material required, but also reduce the amount of time required for such coating material to be dried.
In the prior art, a short dwell coater is typically disposed adjacent to a backing roll such that the web to be coated extends between the short dwell coater blade and the backing roll so that the coating material is applied to the moving web directly supported by the backing roll.
With the aforementioned arrangement using a backing roll, there exists a problem when operating such a coater at relatively high speeds over 3,000 feet per minute. The aforementioned problem is caused by the radius of the backing roll which generates a centrifugal force within the coating material being applied. Such centrifugal force generated within the coating material causes secondary or back flow within the coating chamber of the short dwell coater. Such secondary flow tends to disturb the primary flow of coating material from the coating chamber through the outlet onto the moving web causing uneven distribution of coating material in a cross-machine direction. This uneven distribution contributes to coating weight non-uniformities in the resultant coated web.
The present invention overcomes the aforementioned problem of the prior art arrangements by providing a backing blanket extending in a closed loop around a first and second guide roll. The web of paper is supported by the backing blanket and the short dwell coater is disposed adjacent to the planar run of the backing blanket between the guide rolls. By this means, because of the absence of any centrifugal force tending to throw the coating material away from the backing blanket, the aforementioned deleterious secondary flows are inhibited.
Therefore, it is a primary objective of the present invention to overcome the aforementioned inadequacies of the prior art proposals and to provide a coater apparatus that makes a considerable contribution to the art of applying coating material to a moving web of paper.
Another object of the present invention is the provision of a coater apparatus which includes a first and a second guide roll and a backing blanket extending in an endless loop between the guide rolls so that the backing blanket supports the moving web of paper and a short dwell coater is disposed adjacent to the planar run of the backing blanket, thereby inhibiting secondary flows within the coater.
Another object of the present invention is the provision of a coater apparatus in which the backing blanket includes a woven base fabric and a surface layer for supporting a moving web.
Another object of the present invention is the provision of a coater apparatus having a backing blanket which is of composite construction, including a woven base fabric and a woven surface layer having a lower denier than the denier of the base fabric.
Another object of the present invention is the provision of a coater apparatus in which the short dwell coater includes a housing defining a coating chamber. The coating chamber has a coater outlet and a resilient blade disposed adjacent to the outlet. The blade is disposed downstream relative to the outlet for metering and smoothing the coating material onto the moving web such that the secondary flows that would be generated within the coating chamber with the use of a backing roll are inhibited by the use of the planar disposition of the moving web supported by the blanket.
Another object of the present invention is the provision of a coater apparatus in which the resilient blade is disposed adjacent to the second guide roll such that the web and the backing blanket are disposed between the blade and the second guide roll so that the blade is fully supported by the second guide roll. The outlet is disposed upstream relative to the second guide roll and between the guide rolls.
Other objects and advantages of the present invention will be readily apparent to those skilled in the art by a consideration of the detailed description contained hereinafter taken in conjunction with the annexed drawings.